1. Field of Invention
This disclosure relates to a bearing for a roller cone bit. Specifically, the present disclosure concerns a hydrostatic bearing assembly employing a sealed lubricant reservoir located in a high stress region of the bearing.
2. Description of Prior Art
Drill bits used in drilling of subterranean well bores typically comprise drag bits and roller cone bits. Roller cone bits typically comprise a body having legs extending downward and a head bearing extending from the leg towards the axis of the bit body. Frusto-conically shaped roller cones are rotatably mounted on each of these journals and are included with cutting teeth on the outer surface of these cones. Because of the high stresses incurred during drilling operations, the bearing mating surfaces within the bit require a bearing material or a surface treatment to sustain the loads and extend the bit life.
FIG. 1 provides in a side cross-sectional view an example of a portion of a roller cone drill bit 10. In this example the roller cone bit 10 includes a body 11 having a bearing pin 14 depending from its lower end. A roller cone 12 is shown rotatingly mated onto the bearing pin 14. A set of balls 16 is provided in an annular opening formed between the cone 12 and the head 14 and serves as a cone-retention system. A secondary purpose of the balls 16 is to provide a rolling surface for facilitating rotation of the cone 12.
Compacts 20 are shown extending outward from the cone 12 surface. Rotating the bit 10 on a wellbore bottomhole BH in turn rotates the cone 12 to engage the compacts 20 with the bottomhole formation 21. Adding weight on bit force with cone 12 rotation crushes the bottomhole formation 21 under the applied force of the compacts 20. Traditionally, a journal bearing element 18 is disposed in a recess 19 circumferentially formed within the head section 14. The journal bearing element 18 accommodates the cone 12 rotation and the forces transferred between the cone 12 and the head section 14. A significant amount of the transferred forces exerted on head section 14 and the roller cone 12 contact surface are concentrated in the region between the head 14 and the bottomhole BH. For the purposes of discussion herein, this region is referred to as the lower portion 22. The concentrated force on the lower portion 22 urges lubricant between the head 14 and roller cone 12 out of the lower portion 22 thereby causing metal to metal contact, that in turn accelerates material wear along the head 14 and roller cone 12 contact surface in the lower portion 22.